Ubiquitination of Zeta-associated Protein of 70 kDa Regulates the Activation of T Cell Receptor-proximal Signaling Pathways.

摘要

The tyrosine kinase Zap-70 is a key regulator of T cell receptor (TCR) signaling downstream of antigen presentation. It plays an essential role in signaling pathways involved in T cell development and function. Loss of Zap-70 results in severe developmental and functional defects in the T cell compartment. Lack of Zap-70 or a complete loss of its function leads to the development of rare severe primary immunodeficiencies, while more common polymorphisms that lead to subtle defects in TCR signaling are paradoxically associated with autoimmunity.;The coordinated regulation of Zap-70 kinase activity is critical for proper T cell proliferation, differentiation, and effector function during an immune response. Zap-70 is cytosolic in unstimulated T cells, but is rapidly recruited to the TCR complex following receptor stimulation. Its activity is regulated both by binding to subunits of the TCR and by phosphorylation on multiple tyrosine residues. We and others have previously reported that Zap-70 is also ubiquitinated following TCR stimulation. Herein, we report the identification and functional characterization of novel Zap-70 ubiquitination sites. Three sites, including Lys-193, Lys-217, and Lys-376, displayed greater than 20-fold increase in modification levels following TCR stimulation. Abrogation of Lys-217 ubiquitination results in increased kinase activation and enhanced activation of downstream signaling pathways. Increased activation of TCR signaling pathways is accompanied by elevated IL-2 production following TCR stimulation. These data suggest that Zap-70 ubiquitination contributes to the regulation of Zap-70 signaling following TCR stimulation. Importantly, we also demonstrate the appearance of ubiquitinated Zap 70 in primary human T cells, indicating the likelihood that Zap-70 ubiquitination plays a widespread and critical role in regulating Zap-70 signaling functions as part of a mechanism that controls the extent of T cell activation following antigen stimulation.